A High-Performance Sailplane Airfoil with Variable Upper-Surface Contour

Abstract

In a feasibility study, an airfoil was developed that satisfies the complex requirements of high performance sailplanes with a variable upper-surface contour.  The base wing, which includes the non-deformable lower surface, an internal torsion box, as well as a spar, is designed to carry the loads and moments typical of a l5-meter span Racing-Class sailplane.  The flexible skin of the upper-surface is attached to the leading edge of the base airfoil and to four linkage points of a mechanical drive.  The chordwise stiffness distribution of the composite skin is tailored so that the two desired contours are accomplished in conjunction with the mechanical drive.  The thin version has a maximum thickness of 11.8% of chord, while the thick airfoil 14.4% of chord.  A cruise flap allows a further adjustment of the airfoil performance to different flight speeds.  The performance estimation for a Racing-Class sailplane with the new airfoil shows significant increases in average cross-country speeds that are, depending on the weather model, up to 5% faster than using conventional airfoils.